Method of forming dual-cure nanostructure transfer film

ABSTRACT

A method of forming a transfer film is described. The transfer film includes a template layer having a first major surface and an opposing second major surface. The second major surface includes a structured non-planar release surface. A backfill layer is disposed upon and conforms to the non-planar structured surface. The backfill layer includes a first cross-linked polymer and a plurality of multifunctional monomers, which cure via different and independent curing mechanisms.

BACKGROUND

Nanostructures and microstructures on glass substrates are used for avariety of applications in display, lighting, architecture andphotovoltaic devices, for example. In display devices the structures canbe used for light extraction or light distribution. In lighting devicesthe structures can be used for light extraction, light distribution, anddecorative effects. In photovoltaic devices the structures can be usedfor solar concentration and antireflection. Patterning or otherwiseforming nanostructures and microstructures on large glass substrates canbe difficult and cost-ineffective.

Lamination transfer methods that use a structured backfill layer insidea nanostructured sacrificial template layer as a lithographic etch maskhave been disclosed. The backfill layer can be a glass-like material.However, these methods require removing the sacrificial template layerfrom the backfill layer while leaving the structured surface of thebackfill layer substantially intact. The sacrificial template layer istypically removed by a dry etching process using oxygen plasma, athermal decomposition process, or a dissolution process.

SUMMARY

The present disclosure relates to dual-cure structured transfer film andmethod of forming the same. The structured transfer film is partiallycured to form a stable, tacky film. This tacky film is laminated onto areceptor substrate and fully cured to impart stable nanostructure and/ormicrostructure to the receptor substrate. The structured transfer filmis formed by a curing one of a first multifunctional monomer or a secondmultifunctional monomer. The structured transfer film is laminated to areceptor substrate and then the other multifunctional monomer is curedto form an interpenetrating network. The first multifunctional monomeris cured with a one of, a free-radical or cationic cure mechanism, andthe second multifunctional monomer is cured with a one of, afree-radical or cationic cure.

In one aspect, a method of forming a transfer film includes coating abackfill composition onto a structured non-planar template layer to forma backfill layer conforming to the non-planar structured surface. Thecomposition includes multifunctional epoxy monomers, multifunctionalacrylate monomers, and a molecule having acrylate and epoxyfunctionalities. Then the method includes curing the multifunctionalepoxy monomers to form a cross-linked epoxy polymer with themultifunctional acrylate monomers dispersed therein and forming atransfer film.

In another aspect, a method of forming a transfer film includes coatinga backfill composition onto a structured non-planar template layer toform a backfill layer conforming to the non-planar structured surface.The composition includes multifunctional epoxy monomers, multifunctionalacrylate monomers, and a molecule having acrylate and epoxyfunctionalities. Then the method includes curing the multifunctionalacrylate monomers to form a cross-linked acrylate polymer with themultifunctional epoxy monomers dispersed therein and forming a transferfilm.

In another aspect, a method includes laminating the backfill layer ofthe transfer film, described herein, onto a receptor substrate andcuring the multifunctional acrylate monomers to form a cross-linkedacrylate polymer interpenetrating the cross-linked epoxy polymerdefining a fully cured structured layer or curing the multifunctionalepoxy monomers to form a cross-linked epoxy polymer interpenetrating thecross-linked acrylate polymer defining a fully cured light transmissionlayer.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a process of making the dual-curetransfer tape and structured receptor substrate;

FIG. 2 is a schematic diagram of an illustrative OLED device.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration several specific embodiments. It is to be understoodthat other embodiments are contemplated and may be made withoutdeparting from the scope or spirit of the present disclosure. Thefollowing detailed description, therefore, is not to be taken in alimiting sense.

All scientific and technical terms used herein have meanings commonlyused in the art unless otherwise specified. The definitions providedherein are to facilitate understanding of certain terms used frequentlyherein and are not meant to limit the scope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the properties sought tobe obtained by those skilled in the art utilizing the teachingsdisclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise.

As used in this specification and the appended claims, the term “or” isgenerally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

As used herein, “have”, “having”, “include”, “including”, “comprise”,“comprising” or the like are used in their open ended sense, andgenerally mean “including, but not limited to”. It will be understoodthat “consisting essentially of”, “consisting of”, and the like aresubsumed in “comprising,” and the like.

In this disclosure:

“curing” refers to cross-linking functional groups of proximate monomersor polymers;“actinic radiation” refers to wavelengths of radiation that can curepolymers and can include ultraviolet, visible, and infrared wavelengthsand can include digital exposures from rastered lasers, thermal digitalimaging, and electron beam scanning;“AMOLED” refers to active matrix organic light-emitting diode;“LED” refers to a light-emitting diode;“microstructures” refers to structures that range from about 0.1 μm toabout 1000 μm in their longest dimension. In this disclosure, the rangesof nanostructures and microstructures necessarily overlay;“nanostructures” refers to features that range from about 1 nm to about1000 nm in their longest dimension.

The present disclosure relates to dual-cure structured transfer film.The structured transfer film is partially cured to form a stable, tackyfilm. This tacky film is laminated onto a receptor substrate and fullycured to impart stable nanostructure and/or microstructure to thereceptor substrate. The transfer film utilizes a dual-curable resinformulation coated on the topography of a structured liner. The firstcuring stage of the resin forms a stable, tacky film that takes theshape of the inverse pattern of the structured liner, having a planartop surface that can be covered with a release liner for transport andsubsequent lamination. The planar surface of the tacky film can belaminated and cured against a receptor substrate to fully cure the resinand enhance adhesion to the receptor substrate, then the structuredliner can be removed to leave behind a structure (nanostructure and/ormicrostructure) on the receptor substrate. The resulting structure isthermally stable (has a thermal decomposition temperature of greaterthan 100 degrees centigrade or greater than 200 degrees centigrade orgreater than 250 degrees centigrade) and has excellent resistance tosolvents due to the interpenetrating and inter-reacted polymer network.The first cure mechanism is different than and independent of the secondcure mechanism. In many embodiments the first cure type is a cationiccure mechanism and the second cure mechanism is a free-radical curemechanism. In other embodiments, the first cure mechanism is afree-radical cure mechanism and the second sure mechanism is a cationiccure mechanism. One embodiment includes a thermal cationic first stagecure and then an actinic radiation (UV) free-radical cure to fully curethe laminated structure to the substrate. The dual-curable resinformulation includes an epoxy component, an acrylate component and acompatibilizer molecule that includes epoxy and acrylatefunctionalities. The epoxy component can be a multi-functional moleculeand the acrylate component can be a multi-functional molecule. Thetransfer film and the resulting structure (light transmission layer) onthe substrate has a haze value that is less than 2% or less than 1% anda visible light transmission that is greater than 85%. While the presentdisclosure is not so limited, an appreciation of various aspects of thedisclosure will be gained through a discussion of the examples providedbelow.

Structured lamination transfer films and methods are disclosed thatenable the fabrication of structured solid surfaces using lamination.The methods involve replication of a film, layer, or coating in order toform a structured template layer (also referred to as “structurednon-planar template layer”). The replication can be performed against amaster using any microreplication techniques known to those of ordinaryskill in the art of microreplication. These techniques can include, forexample, embossing, cast and cure of a prepolymer resin (using thermalor photochemical initiation), or hot melt extrusion. Typicallymicroreplication involves casting of a photocurable prepolymer solutionagainst a template followed by photopolymerization of the prepolymersolution. In this disclosure, “nanostructured” refers to structures thathave features that are less than 1 μm, less than 750 nm, less than 500nm, less than 250 nm, 100 nm, less than 50 nm, less than 10 nm, or evenless than 5 nm. “Microstructured” refers to structures that havefeatures that are less than 1000 μm, less than 100 μm, less than 50 μm,or even less than 5 μm. Hierarchical refers to structures with more thanone size scale include microstructures with nanostructures (e.g. amicrolens with nanoscale moth eye antireflection features). Laminationtransfer films have been disclosed, for example, in Applicants' pendingpublished application, US 2014/0021492, entitled “STRUCTURED LAMINATIONTRANSFER FILMS AND METHODS”.

FIG. 1 is a schematic diagram of a process of making the dual-curetransfer tape and structured receptor substrate. A structured non-planartemplate is formed or disposed on a carrier 101, as described above. Thestructured non-planar template layer 103 includes a release surfacethat, in many embodiments, is a thin layer of release coating (notshown) deposited by, for example, plasma enhanced chemical vapordeposition. In some embodiments, release properties may be inherent tothe structured template layer.

The resulting structure is then coated with an uncured backfillcomposition 105. The uncured backfill composition 105 intimatelycontacts the structured non-planar template layer 103. The backfillcomposition includes multi-functional epoxy monomers, multifunctionalacrylate monomers, and a compatibilizing molecule having acrylate andepoxy functionalities. In many embodiments, the backfill composition isat least 95% wt monomer and compatibilizing molecule or at least 98% wtmonomer and compatibilizing molecule or substantially monomer andcompatibilizing molecule.

The multi-functional epoxy monomers, multifunctional acrylate monomershave different and independent curing mechanisms. Thus, the uncuredbackfill composition can include a cationic initiator and a free-radicalinitiator. In one example, the multi-functional epoxy monomers have acationic curing mechanism, and the multifunctional acrylate monomershave an independent free-radical curing mechanism.

In one embodiment, the multifunctional acrylate monomers have a photofree-radical (via UV light and a radical photoinitiator) curingmechanism and the multi-functional epoxy monomers have a cationicthermal (via heat and a thermal acid generator) curing mechanism. Inanother embodiment, the multifunctional acrylate monomers have a thermalfree-radical (via heat and a thermal acid generator) curing mechanismand the multi-functional epoxy monomers have a photo-cationic (via UVlight and a radical photoinitiator) curing mechanism.

Three stages are associated with the formation of the final filmarticle. Stage A (A-Stage) is defined as the starting formulation inwhich no or negligible cure has occurred. Stage B (or B-Stage) isdefined as the state in which the first of the two sets of curablegroups has cured to an extent sufficient to give a film capable offunctioning as a pressure sensitive adhesive at the required surface(partial cure). Stage C (or C-Stage) is defined as the state in whichthe second of the two sets of curable groups has cured to an extent thatthe film maintains the template pattern and releases from the template(full cure).

In illustrative embodiments, the transfer film is formed by curing themultifunctional epoxy monomers to form a cross-linked epoxy polymer withthe multifunctional acrylate monomers dispersed therein. This partiallycured (or b-stage) film has an elastic modulus value that is less than0.3×10⁵ Pa which provides a pressure-sensitive adhesive-like tack to avariety of surfaces that is stable over time. In addition this partiallycured (or b-stage) film has good wet-out and adhesion to the structurednon-planar template layer 103.

The partially cured (or b-stage) film should have a modulus value thatis no more than Dahlquist Criterion (0.3×10⁵ Pa or 3×10⁶ dynes/cm² atroom temperature when measured at a frequency of about 1 Hz), whichprovides a pressure-sensitive adhesive-like tack to a variety ofsurfaces that is stable over time. This is a criterion for tack and hasbeen given the name “Dahlquist criterion for tack” after the scientistwho studied this phenomenon (see Dahlquist, C. A., in AdhesionFundamentals and Practice, The Ministry of Technology (1966) McLaren andSons, Ltd., London). Above this modulus, adhesive failure occurs asobserved from the small strains at separation.

In other illustrative embodiments, the transfer film is formed by curingthe multifunctional acrylate monomers to form a cross-linked acrylatepolymer with the multifunctional epoxy monomers dispersed therein. Thispartially cured (or b-stage) film has an elastic modulus value thatclose to the above mentioned Dahlquist criterion at the processingtemperature of 60° C. which provides a pressure-sensitive adhesive-liketack to a variety of surfaces that is stable over time. Additionally,the b-staged film has a glass transition temperature at or below roomtemperature to help “wet-out” of the film onto the receptor substrate.In addition this partially cured (or b-stage) film has some adhesion tothe structured non-planar template layer 103.

In many embodiments, the partially cured (or b-stage) film has a hazevalue of less than 2% or less than 1% and a visible light transmissionof greater than 85% or greater than 90%. In many embodiments, thepartially cured (or b-stage) film has a glass transition temperature ofless than 30 degrees centigrade or less than 25 degrees centigrade orless than 20 degrees centigrade.

Once the stable partially cured (or b-stage) film is formed, an optionalrelease liner 104 can be applied to the stable partially cured (orb-stage) film for protection during transport and subsequent processing.The release liner 104 can be disposed on onto a planar major surface ofthe backfill layer 105 where the backfill layer 105 separates therelease liner 104 from the structured non-planar release surface 103.The optional release liner 104 is removed from the stable partiallycured (or b-stage) film before the transfer film is laminated onto thereceptor substrate 110.

The receptor substrate 110 can be optionally coated with an adhesionpromotion layer 112 to aid in the adhesion of the stable partially cured(or b-stage) film and resulting fully cured structured lighttransmission layer. The adhesion promotion layer 112 can be formed inany useful manner such as spin coating, dip coating, spraying, plasmapolymerization or via other deposition processes.

The stable partially cured (or b-stage) film is laminated onto areceptor substrate 110. This laminated film is cured to crosslink theremaining multifunctional monomers and form interpenetratingcross-linked polymer networks defining a fully cured structured layer.The fully cured structured layer can then release from the structurednon-planar template layer 103.

FIG. 2 is a schematic diagram of an illustrative OLED device 200 colorfilter layer 210. The backfill layer 205 (partially or cully cured) canbe disposed on or coupled to the color filter layer 210. One or morelayers, such as a planarization layer 211, can couple the color filterlayer 210 to the backfill layer 205 (partially or cully cured). A glasssubstrate 201 can be coupled to the opposing side of the color filterlayer 210. A high refractive index layer 202 (e.g., R.I. greater than1.6) can be disposed on the structured surface of the backfill layer 205(partially or cully cured). The functional layers of the OLED are notillustrated but it is understood that these layers can be adjacent toeither side of the illustrative OLED device 200 layers illustrated.

The fully cured structured layer has a haze value of less than 2% orless than 1% and a visible light transmission greater than 85% orgreater than 90% and a glass transition temperature greater than 150degrees centigrade or greater than 200 degrees centigrade or greaterthan 250 degrees centigrade. The fully cured structured layer can bereferred to as a “structured light transmission layer” and be stable attemperatures of 100 degrees centigrade or greater, or be stable attemperatures of 150 degrees centigrade or greater, or be stable attemperatures of 200 degrees centigrade or greater, or be stable attemperatures of 250 degrees centigrade or greater, for at least 10minutes. The fully cured structured layer can be solvent stable andresistant to IPA, MEK, toluene, heptane, methoxypropanol, and othersolvents. The fully cured structured layer can be mechanically stablefor example able to withstand 10 min of sonication in water and/or IPA.The fully cured structured layer can have a visible light refractiveindex of about 1.5±0.1.

In some embodiments, the epoxy monomers are first cured to form thetransfer film and then the acrylate monomers are cured to form across-linked acrylate polymer interpenetrating the cross-linked epoxypolymer defining a fully cured structured layer. In some of theseembodiments, the cross-linked epoxy polymer was cured (b-stage) via acationic mechanism and the multifunctional acrylate monomers are cured(c-stage) via a free-radical mechanism.

In other embodiments, the acrylate monomers are first cured to form thetransfer film and then the epoxy monomers are cured to form across-linked epoxy polymer interpenetrating the cross-linked acrylatepolymer defining a fully cured structured layer. In some of theseembodiments, the cross-linked acrylate polymer was cured (b-stage) via afree-radical mechanism and the multifunctional epoxy monomers are cured(c-stage) via a cationic mechanism.

In many embodiments, a plurality of compatibilizer molecules having anacrylate group bonded to the cross-linked acrylate polymer and an epoxygroup bonded to the cross-linked epoxy polymer are present in the fullycured structured layer.

Multifunctional Acrylate Monomers

A “polyfunctional acrylate” or “multifunctional acrylate” component canbe the reaction product of aliphatic polyhydroxy compounds and(meth)acrylic acids.

(Meth)acrylic acids are unsaturated carboxylic acids which include, forexample, those represented by the following basic formula:

where R is a hydrogen atom or a methyl group.

Polyfunctional (i.e., multifunctional) acrylates can be a monomer or anoligomer. The term “monomer” refers to a small (low-molecular-weight)molecule with a capability of forming chemical bonds with the same orother monomers in such manner that long chains (polymeric chains ormacromolecules) are formed. The term “oligomer” refers to a polymermolecule having 2 to 10 repeating units (e.g., dimer, trimer, tetramer,and so forth) having a capability of forming chemical bonds with thesame or other oligomers in such manner that longer polymeric chains canbe formed therefrom. Mixtures of monomers and oligomers also could beused as the polyfunctional acrylate component. It is preferred that thepolyfunctional acrylate component be monomeric.

Representative polyfunctional acrylate monomers include, by way ofexample and not limitation: ethylene glycol diacrylate, ethylene glycoldimethacrylate, hexanediol diacrylate, triethylene glycol diacrylate,trimethylolpropane triacrylate, ethoxylated trimethylolpropanetriacrylate, glycerol triacrylate, pentaerthyitol triacrylate,pentaerythritol trimethacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, and neopentylglycol diacrylate.Mixtures and combinations of different types of such polyfunctionalacrylates also can be used. The term “acrylate”, as used herein,encompasses acrylates and methacrylates.

Useful commercially available polyfunctional acrylates include atrimethylolpropane triacrylate having the trade designation “SR351,” anethoxylated trimethylolpropane triacrylate having the trade designation“SR454,” a pentaerythritol tetraacrylate having the trade designation“SR295,” a cyclohexane dimethonal diacrylate having the tradedesignation “SR833S” and a neopentylglycol diacrylate having the tradedesignation “SR247,” and all of these being commercially available fromSartomer Co., Exton, Pa.

The polyfunctional acrylate monomers cure quickly into a network due tothe multiple functionalities available on each monomer. If there is onlyone acrylate functionality, a linear, non-networked molecule will resultupon cure of the material. Polyfunctional acrylates having afunctionality of two or more are preferred in this invention toencourage and promote the desired polymeric network formation.

The backfill layer or light transmitting layer can have any usefulamount of polyfunctional acrylate. In many embodiments the backfilllayer or light transmitting layer has 40 to 90% wt polyfunctionalacrylate. In some embodiments the backfill layer or light transmittinglayer has 60 to 80% wt polyfunctional acrylate.

Multifunctional Epoxy Monomers

Useful epoxy resins include any organic compounds having at least oneoxirane ring, i.e.,

polymerizable by a ring opening reaction. Such materials, broadly calledepoxides, include both monomeric and oligomeric epoxides and can bealiphatic, cycloaliphatic, or aromatic. They can be liquid or solid orblends thereof. These materials generally have, on the average, at leasttwo epoxy groups per molecule (preferably more than two epoxy groups permolecule). The polymeric epoxides include linear polymers havingterminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkyleneglycol), polymers having skeletal oxirane units (e.g., polybutadienepolyepoxide), and polymers having pendent epoxy groups (e.g., a glycidylmethacrylate polymer or copolymer).

Useful epoxy resins include those which contain cyclohexene oxide groupssuch as the epoxycyclohexanecarboxylates, typified by3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methycyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference may bemade to U.S. Pat. No. 3,117,099, incorporated herein by reference.

Further epoxy resins which are particularly useful include glycidylether monomers of the formula:

where R′ is alkyl or aryl and n is an integer of 2 to 6. Examples arethe glycidyl ethers of polyhydric phenols obtained by reacting apolyhydric phenol with an excess of chlorohydrin such asepichlorohydrin, e.g., the diglycidyl ether of2,2-bis-2,3-epoxypropoxyphenol propane. Further examples of epoxides ofthis type which can be used in the practice of this invention aredescribed in U.S. Pat. No. 3,018,262, incorporated herein by reference.

There is a host of commercially available epoxy resins which can beuseful. In particular, epoxides which are readily available includeoctadecylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexeneoxide, glycidol, glycidyl-methacrylate, diglycidyl ether of Bisphenol A(e.g., those available under the trade designations “EPON 828,” “EPON1004,” and “EPON 1001F” from Shell Chemical Co., and “DER-332” and“DER-334,” from Dow Chemical Co.), diglycidyl ether of Bisphenol F(e.g., “ARALDITE GY281” from Ciba-Geigy), vinylcyclohexene dioxide(e.g., having the trade designation “ERL 4206” from Union CarbideCorp.), 3,4-epoxycyclohexyl-methyl-3,4-epoxycyclohexene carboxylate(e.g., having the trade designation “ERL-4221” from Union CarbideCorp.), 2-(3,4-epoxycyclo-hexyl-5,5-spiro-3,4-epoxy)cyclohexane-metadioxane (e.g., having the trade designation “ERL4234”from Union Carbide Corp.), bis(3,4-epoxy-cyclohexyl) adipate (e.g.,having the trade designation “ERL-4299” from Union Carbide Corp.),dipentene dioxide (e.g., having the trade designation “ERL4269” fromUnion Carbide Corp.), epoxidized polybutadiene (e.g., having the tradedesignation “OXIRON 2001” from FMC Corp.), silicone resin containingepoxy functionality, epoxy silanes, e.g.,beta-3,4-epoxycyclohexylethyltri-methoxy silane andgamma-glycidoxypropyltrimethoxy silane, commercially available fromUnion Carbide, flame retardant epoxy resins (e.g., having the tradedesignation “DER-542,” a brominated bisphenol type epoxy resin availablefrom Dow Chemical Co.), 1,4-butanediol diglycidyl ether (e.g., havingthe trade designation “ARALDITE RD-2” from Ciba-Geigy), hydrogenatedbisphenol A-epichlorohydrin based epoxy resins (e.g. having the tradedesignation “EPONEX 1510” from Shell Chemical Co.), and polyglycidylether of phenol-formaldehyde novolak (e.g., having the trade designation“DEN-431” and “DEN-438” from Dow Chemical Co.).

Latent curative systems which may be useful in the present disclosureinclude those conventionally used for curing epoxy resin compositionsand forming cross-linked polymer networks, including hydrazides such asaminodihydrazide, adipic dihydrazide, isopthalyl dihydrazide; guanidinessuch as tetramethyl guanidine; and, dicyandiamide.

The amount will vary from resin to resin and is generally to be providedin such an amount as to be effective in causing substantially completecuring within a desired length of time. A typical composition accordingto the present disclosure includes about 1-10%, by weight of latenthardener based on the total weight of the one-part curable epoxycomposition. It will be understood that the final properties of thecured composition will be greatly influenced by the relative amounts ofcross-linking and epoxy chain extension caused respectively by thelatent hardener.

In some embodiments, the latent curative system has two or more latentaccelerators selected from at least one of substituted ureas,substituted imidazoles, and combinations thereof. In some embodiments,the components of the resin miscible first curative can be pre-blendedand then added to the heat curable epoxy resin. In some embodiments, thecomponents of the resin miscible first curative can be separately addedto the heat curable epoxy resin

In some embodiments, the ureas are selected from bis-substituted ureas.In some embodiments, the imidazoles are selected from 1-N substituted-,2-C substituted-imidazoles, and metal imidazolate salts as described inU.S. Pat. No. 4,948,449, having a melting point greater than 200° C.Suitable curatives are commercially available under the tradedesignations CUREZOL 2PHZ-S, CUREZOL 2MZ-AZINE, and CUREZOL 2MA-OK fromAir Products and Chemicals; under the trade designation ARADUR 3123 fromHuntsman Advanced Materials; and under the trade designation OMICUREU-35 and OMICURE U-52 from CVC Thermoset Specialties. To achieve fastcuring, both an initiator and an activator are generally required. Whena two-part system is formulated, one part will contain an initiator andthe other part an activator.

Activators that can be used consist of tertiary amines, amine/aldehyde(or ketone) condensates, mercapto compounds, or transition metalcompounds. Examples of useful tertiary amines are: N,N-dimethylaniline,N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-diethyl-p-toluidine,or N,N-diisopropyl-p-toluidine. Examples of mercapto compounds are:2-mercaptobenzimidazole, allylthiourea, and ethylene thiourea. Examplesof useful amine/aldehyde condensates are: aniline/butyraldehyde,butylamine/benzaldehyde, and butylamine/benzil. Examples of transitionmetal compounds are: copper naphthenate, iron naphthenate; cobaltnaphthenate, nickel naphthenate, manganese naphthenate; copperoctanoate; iron hexanonate, iron propionate; copper oxide, manganeseoxide, vanadium oxide, molybdenum dioxide; and vanadium oxide(acetylacetonate)₂, and molybdenum oxide (acetylacetonate)₂.

The backfill layer or light transmitting layer can have any usefulamount of polyfunctional epoxy. In many embodiments the backfill layeror light transmitting layer has 0.1 to 25% wt polyfunctional epoxy. Insome embodiments the backfill layer or light transmitting layer has 10to 20% wt polyfunctional epoxy.

Compatibilizer Molecules

Some molecules can be used to compatibilize the two different phasespresent in the transfer film. These molecules typically have at leastone of each functional group represented from among the two phases.Representative molecules may have one terminal epoxy group and oneterminal acrylate group, for example. Examples of these moleculesinclude partially acrylated bisphenol A diglycidyl ether (otherwiseknown as “CN-153” Sartomer Corp, Exton, Pa.), 2-hydroxybutylglycidylacrylate (“4-HBAGE” Nippon Kasei Chemical, Tokyo, Japan), glycidyl(meth)acrylate, 3,4-Epoxycyclohexylmethyl methacrylate (sold as“CYCLOMER M100 (Daicel Corp, Osaka, Japan). Rather than having twogroups which are chemically similar to the phases in the transfer film,it may also possible for one of the functional groups in thecompatibilizer molecule to be able to chemically react with one of thephases in the transfer film. For example, molecules with primaryhydroxyl functionality are known to chemically react with epoxidefunctionalities. Therefore, molecules with terminal hydroxylfunctionalities and terminal acrylate functionalities may be used.Examples of these molecules include pentaerythritol tetraacrylate(“SR444” Sartomer, Exton, Pa.).

Other oligomers include acrylated epoxies such as diacrylated esters ofepoxy resins, e.g., diacrylated esters of bisphenol A epoxy resin.Examples of commercially available acrylated epoxies include epoxiesavailable under the trade designations “CMD 3500,” “CMD 3600,” and “CMD3700,” from Radcure Specialties.

Other useful compounds having both epoxy and acrylate functionality, forexample, are described in U.S. Pat. No. 4,751,138 (Tumey et al.), whichis incorporated herein by reference.

The backfill layer or light transmitting layer can have any usefulamount of compatibilizer molecule. In many embodiments the backfilllayer or light transmitting layer has 5 to 40% wt compatibilizermolecule. In some embodiments the backfill layer or light transmittinglayer has 10 to 35% wt compatibilizer molecule. In other embodiments thebackfill layer or light transmitting layer has 15 to 25% wtcompatibilizer molecule.

Another way to quantify the amount of compatibilizer molecule in thebackfill layer or light transmitting layer by relating to or replacingthe epoxy material with compatibilizer material. The compatibilizermolecule can be from 1 to 100% of the molar equivalent to epoxymaterial. The compatibilizer molecule can replace the epoxy material ona 1:1 molar ratio.

The backfill layer or light transmitting layer can have any usefulamount of polyfunctional acrylate, polyfunctional epoxy, andcompatibilizer molecule. In many embodiments the backfill layer or lighttransmitting layer has 40 to 90% wt polyfunctional acrylate, 1 to 30% wtpolyfunctional epoxy, and 5 to 40% wt compatibilizer molecule.

Curing Mechanism

The first multifunctional monomer is cured with a one of, a free-radicalor cationic cure mechanism, and the second multifunctional monomer iscured with one of, a free-radical or cationic cure mechanism, that isdifferent and independent from the first multifunctional monomer curemechanism. The free-radical curing mechanism can be a thermal orphoto-radical curing mechanism. The cationic curing mechanism can be athermal or photo-cationic curing mechanism.

In the case of the free radical curable polyfunctional acrylatecomponent, it is useful to add a free radical initiator to the backfillmaterial, although it should be understood that an electron beam sourcealso could be used to initiate and generate free radicals. The freeradical initiator preferably is added in an amount of 0.1 to 3.0% byweight, based on the total amount of resinous components. Examples ofuseful photoinitiators, that generate a free radical source when exposedto ultraviolet light, include, but are not limited to, organicperoxides, azo compounds, quinones, benzophenones, nitroso compounds,acyl halides, hydrazones, mercapto compounds, pyrylium compounds,triacylimidazoles, acylphosphine oxides, bisimidazoles,chloroalkyltriazines, benzoin ethers, benzil ketals, thioxanthones, andacetophenone derivatives, and mixtures thereof. Examples ofphotoinitiators that generate a source of free radicals when exposed tovisible radiation, are described in U.S. Pat. No. 4,735,632, whichdescription is incorporated herein by reference. A preferred freeradical-generating initiator for use with ultraviolet light is aninitiator commercially available from Lamberti Corporation(Gallarate—VA—Italy) under the trade designation “ESACURE ONE”.

A curing agent to promote polymerization of the epoxy resin can bethermally or photo-activated; that is, the curing agent can be acatalyst activated by actinic radiation (radiation having a wavelengthin the ultraviolet or visible portion of the electromagnetic spectrum)or heat. Useful cationic catalysts generate an acid to catalyze thepolymerization of an epoxy resin. It should be understood that the term“acid” can include either protic or Lewis acids. These cationicinitiators can include a metallocene salt having an onium cation and ahalogen containing complex anion of a metal or metalloid. Other usefulcationic catalysts include a metallocene salt having an organometalliccomplex cation and a halogen containing complex anion of a metal ormetalloid which are further described in U.S. Pat. No. 4,751,138 (e.g.,column 6, line 65 to column 9, line 45), which is incorporated herein byreference. Another example is an organometallic salt and an onium saltdescribed in U.S. Pat. No. 4,985,340 (col. 4, line 65 to col. 14, line50); European Patent Applications 306,161; 306,162, all incorporatedherein by reference. Still other cationic catalysts include an ionicsalt of an organometallic complex in which the metal is selected fromthe elements of Periodic Group IVB, VB, VIB, VIIB and VIIIB which isdescribed in European Patent Application 109,581, which is alsoincorporated herein by reference. Another example of an onium salt whichproduces a thermally activated acid which is useful for curing is knownas “CXC-1612”, an ammonium hexafluoroantimonate salt from KingIndustries (Norwalk, Conn.).

There are other possible orthogonal curing protocols that could be usedin this concept. For example, hydrosilylation between SiH andunsaturated carbon-carbon (alkene, alkyne) can be commonly catalyzed byplatinum compounds. Another example is alcoholysis between SiH and SiOHcommonly catalyzed by platinum compounds. Another useful example isnucleophilic substitution of SiX by SiOH where X is halogen, oxime,carboxylate, alkoxide, commonly catalyzed by a range of acids or bases,tin and titanium compounds. Free radicals could also be used (e.g.peroxide, UV or e-beam) to initiate a reaction between SiCH₃ and SiCH₃.All of these are described in Michael Brook, Silicon in Organic,Organometallic and Polymer Chemistry, Wiley Interscience, 2000, pg282-291.

Latent curative systems can be utilized to cross-link the epoxy moietiesas long as the optical and physical properties of the b-stage andc-stage films are met. Latent curative systems which may be useful inthe present disclosure include those conventionally used for curingepoxy resin compositions and forming cross-linked polymer networks,including hydrazides such as aminodihydrazide, adipic dihydrazide,isopthalyl dihydrazide; guanidines such as tetramethyl guanidine; and,dicyandiamide.

The amount will vary from resin to resin and is generally to be providedin such an amount as to be effective in causing substantially completecuring within a desired length of time. A typical composition accordingto the present disclosure includes about 1-10%, by weight of latenthardener based on the total weight of the one-part curable epoxycomposition. It will be understood that the final properties of thecured composition will be greatly influenced by the relative amounts ofcross-linking and epoxy chain extension caused respectively by thelatent hardener.

In some embodiments, the latent curative system has two or more latentaccelerators selected from at least one of substituted ureas,substituted imidazoles, and combinations thereof. In some embodiments,the components of the resin miscible first curative can be pre-blendedand then added to the heat curable epoxy resin. In some embodiments, thecomponents of the resin miscible first curative can be separately addedto the heat curable epoxy resin.

Applications of Transfer Films

The transfer films (or “lamination transfer films”) disclosed herein canbe used for a variety of purposes. For example, the transfer films canbe used to transfer structured layers in OLED (organic light emittingdiode) devices to improve efficiency or light extraction of the OLED.

Another exemplary application of the lamination transfer films is forpatterning of digital optical elements including microfresnel lenses,diffractive optical elements, holographic optical elements, and otherdigital optics disclosed in Chapter 2 of B. C. Kress, and P. Meyrueis,Applied Digital Optics, Wiley, 2009, on either the internal or externalsurfaces of display glass, photovoltaic glass elements, LED wafers,silicon wafers, sapphire wafers, architectural glass, metal, nonwovens,paper, or other substrates.

The lamination transfer films can also be used to produce decorativeeffects on glass surfaces. For example, it might be desirable to impartiridescence to the surface of a decorative crystal facet. In particular,the glass structures can be used in either functional or decorativeapplications such as transportation glasses, architectural glasses,glass tableware, artwork, display signage, and jewelry or otheraccessories. Durability of the glass structures may be improved by usingthe methods disclosed herein to transfer embedded structures. Also, acoating can be applied over these glass structures. This optionalcoating can be relatively thin in order to avoid adversely affecting theglass structure properties. Examples of such coatings includehydrophilic coatings, hydrophobic coatings, protective coatings,anti-reflection coatings and the like.

Carrier Films

The liner or carrier substrate or film can be implemented with aflexible film providing mechanical support for the transfer film andother layers. One example of a carrier film is polyethyleneterephthalate (PET). In some embodiments, the carrier can include paper,release-coated paper, non-wovens, wovens (fabric), metal films, andmetal foils.

Various polymeric film substrates comprised of various thermosetting orthermoplastic polymers are suitable for use as the carrier. The carriermay be a single layer or multi-layer film. Illustrative examples ofpolymers that may be employed as the carrier layer film include (1)fluorinated polymers such as poly(chlorotrifluoroethylene),poly(tetrafluoroethylene-cohexafluoropropylene),poly(tetrafluoroethylene-co-perfluoro(alkyl)vinylether), poly(vinylidenefluoride-cohexafluoropropylene); (2) ionomeric ethylene copolymerspoly(ethylene-co-methacrylic acid) with sodium or zinc ions such asSURLYN-8920 Brand and SURLYN-9910 Brand available from E. I. duPontNemours, Wilmington, Del.; (3) low density polyethylenes such as lowdensity polyethylene; linear low density polyethylene; and very lowdensity polyethylene; plasticized vinyl halide polymers such asplasticized poly(vinylchloride); (4) polyethylene copolymers includingacid functional polymers such as poly(ethylene-co-acrylic acid) “EAA”,poly(ethylene-co-methacrylic acid) “EMA”, poly(ethylene-co-maleic acid),and poly(ethylene-co-fumaric acid); acrylic functional polymers such aspoly(ethylene-co-alkylacrylates) where the alkyl group is methyl, ethyl,propyl, butyl, et cetera, or CH₃ (CH₂)_(n)— where n is 0 to 12, andpoly(ethylene-co-vinylacetate) “EVA”; and (5) (e.g.) aliphaticpolyurethanes. The carrier layer is typically an olefinic polymericmaterial, typically comprising at least 50 wt-% of an alkylene having 2to 8 carbon atoms with ethylene and propylene being most commonlyemployed. Other body layers include for example poly(ethylenenaphthalate), polycarbonate, poly(meth)acrylate (e.g., polymethylmethacrylate or “PMMA”), polyolefins (e.g., polypropylene or “PP”),polyesters (e.g., polyethylene terephthalate or “PET”), polyamides,polyimides, phenolic resins, cellulose diacetate, cellulose triacetate(TAC), polystyrene, styrene-acrylonitrile copolymers, cyclic olefincopolymers, epoxies, and the like.

Receptor Substrates

Examples of receptor substrates include glass such as display motherglass, lighting mother glass, architectural glass, plate glass, rollglass, and flexible glass (can be used in roll to roll processes). Anexample of flexible roll glass is the WILLOW glass product from CorningIncorporated. Other examples of receptor substrates include metals suchas metal sheets and foils. Yet other examples of receptor substratesinclude sapphire, silicon, silica, and silicon carbide. Yet anotherexample includes fabric, nonwovens, and papers.

Other exemplary receptor substrates include semiconductor materials on asupport wafer. The dimensions of these receptor substrates can exceedthose of a semiconductor wafer master template. Currently, the largestwafers in production have a diameter of 300 mm. Lamination transferfilms produced using the method disclosed herein can be made with alateral dimension of greater than 1000 mm and a roll length of hundredsof meters. In some embodiments, the receptor substrates can havedimensions of about 620 mm×about 750 mm, of about 680 mm×about 880 mm,of about 1100 mm×about 1300 mm, of about 1300 mm×about 1500 mm, of about1500 mm×about 1850 mm, of about 1950 mm×about 2250 mm, or about 2200mm×about 2500 mm, or even larger. For long roll lengths, the lateraldimensions can be greater than about 750 mm, greater than about 880 mm,greater than about 1300 mm, greater than about 1500 mm, greater thanabout 1850 mm, greater than about 2250 nm, or even greater than about2500 mm. Typical dimensions have a maximum patterned width of about 1400mm and a minimum width of about 300 mm. The large dimensions arepossible by using a combination of roll-to-roll processing and acylindrical master template. Films with these dimensions can be used toimpart nanostructures over entire large digital displays (e.g., a 55inch diagonal display, with dimensions of 52 inches wide by 31.4 inchestall).

The receptor substrate can optionally include a buffer layer on a sideof the receptor substrate to which a lamination transfer film isapplied. Examples of buffer layers are disclosed in U.S. Pat. No.6,396,079 (Hayashi et al.), which is incorporated herein by reference asif fully set forth. One type of buffer layer is a thin layer of SiO₂, asdisclosed in K. Kondoh et al., J. of Non-Crystalline Solids 178 (1994)189-98 and T-K. Kim et al., Mat. Res. Soc. Symp. Proc. Vol. 448 (1997)419-23.

A particular advantage of the transfer process disclosed herein is theability to impart structure to receptor surfaces with large surfaces,such as display mother glass or architectural glass. The dimensions ofthese receptor substrates exceed those of a semiconductor wafer mastertemplate. The large dimensions of the lamination transfer films arepossible by using a combination of roll-to-roll processing and acylindrical master template.

An additional advantage of the transfer process disclosed herein is theability to impart structure to receptor surface that are not planar. Thereceptor substrate can be curved, bent twisted, or have concave orconvex features, due to the flexible format of the transfer tape.

Receptor substrates also may include, automotive glass, sheet glass,flexible electronic substrates such as circuitized flexible film,display backplanes, solar glass, metal, polymers, polymer composites,and fiberglass.

Template Layer

The template layer is the layer that imparts the structure to thebackfill layer. It is made up of template materials. The template layercan be formed through embossing, replication processes, extrusion,casting, or surface structuring, for example. The structured surface caninclude nanostructures, microstructures, or hierarchical structures. Insome embodiments, the template layer can be compatible with patterning,actinic patterning, embossing, extruding, and coextruding.

The template layer can include a photocurable material that can have alow viscosity during the replication process and then can be quicklycured to form a permanent crosslinked polymeric network “locking in” thereplicated nanostructures, microstructures or hierarchical structures.Any photocurable resins known to those of ordinary skill in the art ofphotopolymerization can be used for the template layer. The resin usedfor the template layer must be capable, when crosslinked, of releasingfrom the backfill layer during the use of the disclosed structuredtapes, or should be compatible with application of a release layer (seebelow) and the process for applying the release layer. Additionally, theresins used for the template layer must be compatible with theapplication of an adhesion promotion layer as discussed above.

Polymers that can be used as the template layer also include thefollowing: styrene acrylonitrile copolymers; styrene(meth)acrylatecopolymers; polymethylmethacrylate; polycarbonate; styrene maleicanhydride copolymers; nucleated semi-crystalline polyesters; copolymersof polyethylenenaphthalate; polyimides; polyimide copolymers;polyetherimide; polystyrenes; syndiodactic polystyrene; polyphenyleneoxides; cyclic olefin polymers; and copolymers of acrylonitrile,butadiene, and styrene. One preferable polymer is the Lustran SANSparkle material available from Ineos ABS (USA) Corporation. Polymersfor radiation cured template layers include cross linked acrylates suchas multifunctional acrylates or epoxies and acrylated urethanes blendedwith mono- and multifunctional monomers.

Patterned structured template layers can be formed by depositing a layerof a radiation curable composition onto one surface of a radiationtransmissive carrier to provide a layer having an exposed surface,contacting a master with a preformed surface bearing a pattern capableof imparting a three-dimensional microstructure of precisely shaped andlocated interactive functional discontinuities including distal surfaceportions and adjacent depressed surface portions into the exposedsurface of the layer of radiation curable composition on said carrierunder sufficient contact pressure to impart said pattern into saidlayer, exposing said curable composition to a sufficient level ofradiation through the carrier to cure said composition while the layerof radiation curable composition is in contact with the patternedsurface of the master. This cast and cure process can be done in acontinuous manner using a roll of carrier, depositing a layer of curablematerial onto the carrier, laminating the curable material against amaster tool and curing the curable material against the tool usingactinic radiation. The resulting roll of carrier with a patterned,structured template disposed thereon can then be rolled up. This methodis disclosed, for example, in U.S. Pat. No. 6,858,253 (Williams et al.).

For extrusion or embossed template layers, the materials making up thetemplate layer can be selected depending on the particular topography ofthe top structured surface that is to be imparted. In general, thematerials are selected such that the structure is fully replicatedbefore the materials solidify. This will depend in part on thetemperature at which the material is held during the extrusion processand the temperature of the tool used to impart the top structuredsurface, as well as on the speed at which extrusion is being carriedout. Typically, the extrudable polymer used in the top layer has a T_(g)of less than about 140° C., or a T_(g) of from about 85° C. to about120° C., in order to be amenable to extrusion replication and embossingunder most operating conditions. In some embodiments, the carrier filmand the template layer can be coextruded at the same time. Thisembodiment requires at least two layers of coextrusion—a top layer withone polymer and a bottom layer with another polymer. If the top layercomprises a first extrudable polymer, then the first extrudable polymercan have a T_(g) of less than about 140° C. or a T_(g) or of from about85° C. to about 120° C. If the top layer comprises a second extrudablepolymer, then the second extrudable polymer, which can function as thecarrier layer, has a T_(g) of less than about 140° C. or a T_(g) of fromabout 85° C. to about 120° C. Other properties such as molecular weightand melt viscosity should also be considered and will depend upon theparticular polymer or polymers used. The materials used in the templatelayer should also be selected so that they provide good adhesion to thecarrier so that delamination of the two layers is minimized during thelifetime of the transfer film.

The extruded or coextruded template layer can be cast onto a master roll(tool) that can impart patterned structure to the template layer. Thiscan be done batchwise or in a continuous roll-to-roll process.Additionally, a backfill layer can be extruded onto the extruded orcoextruded template layer. In some embodiments, all threelayers—carrier, template, and backfill layers can be coextruded at onceas long as the backfill layer can be separated from the template layerafter processing.

Useful polymers that may be used as the template layer polymer includeone or more polymers selected from the group consisting of styreneacrylonitrile copolymers; styrene (meth)acrylate copolymers;polymethylmethacrylate; styrene maleic anhydride copolymers; nucleatedsemi-crystalline polyesters; copolymers of polyethylenenaphthalate;polyimides; polyimide copolymers; polyetherimide; polystyrenes;syndiodactic polystyrene; polyphenylene oxides; and copolymers ofacrylonitrile, butadiene, and styrene. Particularly useful polymers thatmay be used as the first extrudable polymer include styreneacrylonitrile copolymers known as TYRIL copolymers available from DowChemical; examples include TYRIL 880 and 125. Other particularly usefulpolymers that may be used as the template polymer include styrene maleicanhydride copolymer DYLARK 332 and styrene acrylate copolymer NAS 30,both from Nova Chemical. Also useful are polyethylene terephthalateblended with nucleating agents such as magnesium silicate, sodiumacetate, or methylenebis(2,4-di-t-butylphenol) acid sodium phosphate.

The template layer may be sacrificial meaning that it will be removedfrom the construction at a later time as is the template layer disclosedin Applicants' pending application no. 2014/0021492, entitled“STRUCTURED LAMINATION TRANSFER FILMS AND METHODS”, filed Jul. 20, 2012.However, the method for making the disclosed transfer tapes and articlesmade therefrom do not require that the template layer be sacrificial.

Release Layer

The template layer is removed from the backfill layer. One method toreduce the adhesion of the backfill layer to the template layer is toapply a release coating to the film. One method of applying a releasecoating to the surface of the template layer is with plasma deposition.An oligomer can be used to create a plasma cross-linked release coating.The oligomer may be in liquid or in solid form prior to coating.Typically the oligomer has a molecular weight greater than 1000. Also,the oligomer typically has a molecular weight less than 10,000 so thatthe oligomer is not too volatile. An oligomer with a molecular weightgreater than 10,000 typically may be too non-volatile, causing dropletsto form during coating. In one embodiment, the oligomer has a molecularweight greater than 3000 and less than 7000. In another embodiment, theoligomer has a molecular weight greater than 3500 and less than 5500.Typically, the oligomer has the properties of providing a low-frictionsurface coating. Suitable oligomers include silicone-containinghydrocarbons, reactive silicone containing trialkoxysilanes, aromaticand aliphatic hydrocarbons, fluorochemicals and combinations thereof.For examples, suitable resins include, but are not limited to,dimethylsilicone, hydrocarbon based polyether, fluorochemical polyether,ethylene teterafluoroethylene, and fluorosilicones. Fluorosilane surfacechemistry, vacuum deposition, and surface fluorination may also be usedto provide a release coating.

Plasma polymerized thin films constitute a separate class of materialfrom conventional polymers. In plasma polymers, the polymerization israndom, the degree of cross-linking is extremely high, and the resultingpolymer film is very different from the corresponding “conventional”polymer film. Thus, plasma polymers are considered by those skilled inthe art to be a uniquely different class of materials and are useful inthe disclosed articles.

In addition, there are other ways to apply release coatings to thetemplate layer, including, but not limited to, blooming, coating,coextrusion, spray coating, electrocoating, or dip coating.

Adhesion Promoting Layer Materials

The adhesion promoting layer can be implemented with any materialenhancing adhesion of the transfer film to the receptor substratewithout substantially adversely affecting the performance of thetransfer film. The exemplary materials for the backfill layers can alsobe used for the adhesion promoting layer. Useful adhesion promotingmaterials useful in the disclosed articles and methods includephotoresists (positive and negative), self-assembled monolayers, silanecoupling agents, and macromolecules. In some embodiments,silsesquioxanes can function as adhesion promoting layers. Otherexemplary materials may include benzocyclobutanes, polyimides,polyamides, silicones, polysiloxanes, silicone hybrid polymers,(meth)acrylates, and other silanes or macromolecules functionalized witha wide variety of reactive groups such as epoxide, episulfide, vinyl,hydroxyl, allyloxy, (meth)acrylate, isocyanate, cyanoester, acetoxy,(meth)acrylamide, thiol, silanol, carboxylic acid, amino, vinyl ether,phenolic, aldehyde, alkyl halide, cinnamate, azide, aziridine, alkene,carbamates, imide, amide, alkyne, and any derivatives or combinations ofthese groups. Further, a proprietary silane surface modifier,commercially available from Momentive, Inc. (Waterford, N.Y.) under thetrade designation “SILQUEST A174”, has been found to be particularlysuitable.

Release Liners

The backfill layer can, optionally, be covered with a temporary releaseliner. The release liner can protect the patterned structured backfillduring handling and can be easily removed, when desired, for transfer ofthe structured backfill or part of the structured backfill to a receptorsubstrate. Exemplary liners useful for the disclosed transfer films aredisclosed in PCT Pat. Appl. Publ. No. WO 2012/082536 (Baran et al.).

The liner may be flexible or rigid. Preferably, it is flexible. Asuitable liner (preferably, a flexible liner) is typically at least 0.5mil thick, and typically no more than 20 mils thick. The liner may be abacking with a release coating disposed on its first surface.Optionally, a release coating can be disposed on its second surface. Ifthis backing is used in a transfer article that is in the form of aroll, the second release coating has a lower release value than thefirst release coating. Suitable materials that can function as a rigidliner include metals, metal alloys, metal-matrix composites, metalizedplastics, inorganic glasses and vitrified organic resins, formedceramics, and polymer matrix reinforced composites.

Exemplary liner materials include paper and polymeric materials. Forexample, flexible backings include densified Kraft paper (such as thosecommercially available from Loparex North America, Willowbrook, Ill.),poly-coated paper such as polyethylene coated Kraft paper, and polymericfilm. Suitable polymeric films include polyester, polycarbonate,polypropylene, polyethylene, cellulose, polyamide, polyimide,polysilicone, polytetrafluoroethylene, polyethylenephthalate,polyvinylchloride, polycarbonate, or combinations thereof. Nonwoven orwoven liners may also be useful. Embodiments with a nonwoven or wovenliner could incorporate a release coating. CLEARSIL T50 Release liner;silicone coated 2 mil polyester film liner, available from Solutia/CPFilms, Martinsville, Va., and LOPAREX 5100 Release Liner,fluorosilicone-coated 2 mil polyester film liner available from Loparex,Hammond, Wis., are examples of useful release liners.

The release coating of the liner may be a fluorine-containing material,a silicon-containing material, a fluoropolymer, a silicone polymer, or apoly(meth)acrylate ester derived from a monomer comprising an alkyl(meth)acrylate having an alkyl group with 12 to 30 carbon atoms. In oneembodiment, the alkyl group can be branched. Illustrative examples ofuseful fluoropolymers and silicone polymers can be found in U.S. Pat.No. 4,472,480 (Olson), U.S. Pat. Nos. 4,567,073 and 4,614,667 (bothLarson et al.). Illustrative examples of a useful poly(meth)acrylateester can be found in U.S. Pat. Appl. Publ. No. 2005/118352 (Suwa). Theremoval of the liner shouldn't negatively alter the surface topology ofthe backfill layer.

Additive Materials

The resin used for the transfer film may contain optional additives inorder to improve or maintain performance under a variety of conditions.These may include photoinitiators, polymerization inhibitors, hinderedamine light stabilizers, sensitizers, antioxidants, catalysts,dispersants, leveling agents, and the like.

Fillers

The resin used for the transfer film may contain inorganic fillermaterials to enhance mechanical, thermal, adhesive, or opticalperformance. For example, silica nanoparticles may be used to enhancethe hardness of the resin, without sacrificing the optical transparency.Metal oxide nanoparticles may be used to modify the refractive index ofthe coating without sacrificing the optical transparency of the resinlayer. Examples of these include nanoparticles made from zirconiumoxide, titanium oxide, hafnium oxide, and the like. Said nanoparticlesmay be functionalized with an appropriate ligand in order to enhancecompatibility with the resins used in the transfer film. Examples ofthese may include organoalcohols, carboxylic acids, organosilanes, andthe like.

Objects and advantages of this disclosure are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

Examples

These examples are merely for illustrative purposes only and are notmeant to be limiting on the scope of the appended claims. All parts,percentages, ratios, etc. in the examples and the rest of thespecification are by weight, unless noted otherwise. Solvents and otherreagents used were obtained from Sigma-Aldrich Chemical Company, St.Louis, Mo. unless otherwise noted.

TABLE 1 Glossary Material Abbreviation Description Supplier CELLOXIDE(3,4-Epoxycyclohexane) methyl-3,4- Daicel Corp (Osaka, 2021Pepoxycyclohexylcarboxylate Japan) UVACURE (3,4-Epoxycyclohexane)methyl-3,4- Allnex Corp. (Smyrna, 1500 epoxycyclohexylcarboxylate GA)LA2250 Poly(methylmethacrylate-block-n-butyl Kurarity Co., Houston,acrylate-block-methylmethacrylate) Texas thermoplastic elastomer SR833Stricyclodecane dimethanol diacrylate Sartomer (Exton, PA) CN-153partially acrylated bisphenol A epoxy resin Sartomer (Exton, PA)oligomer Polyacrylate 57.5/35/7.5 w/w/w Iso-octylacrylate/methyl PSAacrylate/acrylic acid) as described in Yang et al., US 2005/0276916 A1.SR368D 70% Trimethylolpropane triacrylate, 30% Sartomer (Exton, PA)tris(2-hydroxy ethyl) isocyanurate triacrylate B-CEABeta-carboxyethylacrylate Allnex Corp. (Smyrna, GA) SR9051 Trifunctionalacidic acrylate adhesion Sartomer (Exton, PA) promoter SILQUEST Gamma-Momentive A174 methacryloxypropyltrimethoxysilane Performance Materials(Waterford, NY) SR399 Dipentaerythritol pentaacrylate Sartomer (Exton,PA) SR238 1,6 hexanediol diacrylate Sartomer (Exton, PA) TMPTATrimethylolpropane triacrylate Sartomer (Exton, PA) OMAN 071p-Octyloxyphenyl)phenyliodonium Gelest Inc (Morrisville,hexafluoroantimonate PA) TEGORAD Silicone acrylate leveling agent EvonikCorp. 2250 (Wallingford, CT) CXC-1612 ammonium hexafluoroantimonate saltKing Industries (Norwalk, CT) DAROCUR2-Hydroxy-2-methyl-1-phenyl-propan-1-one BASF (Ludwigshafen, 1173Germany) ESACURE Difunctional-alpha-hydroxy ketone Lamberti Corp. ONEphotoinitiator (Gallarate-VA-Italy)

TABLE 2 Resin Formulations (grams) Components CE 1 CE 2 Ex. 1 Ex. 2CELLOXIDE 15 15 2021P LA2250 60 SR833S 40 50 60 40 CN-153 20 20Polyacrylate PSA 30 SR368D 35 B-CEA 20 SR9051 5 SILQUEST A174 2 TEGO RAD2250 0.03 0.03 CXC-1612 0.6 0.6 DAROCUR 1173 1 1 ESACURE ONE 1 1Methoxypropanol 30 30 Toluene 400

Substrate Preparation

Glass slides were rinsed well with acetone and isopropanol and driedwith cleanroom wipe. The slides were exposed to an oxygen plasma in aYES G1000 system (O₂=60 sccm, time=3 min, RF=300 W) to remove anyresidual hydrocarbon contamination and expose surface silanol groups.The slides were kept dehydrated in a hot oven >100 C until ready foruse, and then placed in a dessicator with 3 drops of3-methacryloxypropyltrimethoxysilane (“SILQUEST A-174”), which was thenplaced in an oven at 80 degrees C. for four hours. After removal fromthe dessicator, a change in the water contact angle was observed,signifying deposition of a monolayer of the silane. Any silane that wasnot covalently bound to the glass slide was washed away with acetone andisopropanol. Example #1 did not require the SILQUEST A-174 adhesionpromoter depoised on a glass slide.

Template/Microstructured Release Liner Preparation

The base film was 2-mil PET, primed with a UV cured primer comprising50/50 blend of UVACURE 1500 and TMPTA with 1% OMAN 071 photoinitiator.The replicating resin was a 75/25 blend of SR 399 and SR238 with aphotoinitiator package comprising 1% Darocur 1173, 1.9% triethanolamine,0.5% OMAN 071, and 0.3% methylene blue. Replication of the resin wasconducted at 20 fpm with the tool temperature at 137 deg F. Radiationfrom a Fusion “D” lamp operating at 600 W/in was transmitted through thefilm to cure the resin while in contact with the tool. The compositefilm was removed from the tool and the patterned side of the film waspost UV cured using a Fusion “D” lamp operating at 360 W/in while incontact with a chill roll heated to 100 deg F. The microstructurecontained an optical diffraction pattern that had multiple pitches (400,500, and 600 nm).

The replicated template film was primed with argon gas at a flow rate of250 standard cc/min (SCCM), a pressure of 25 mTorr and RF power of 1000Watts for 30 seconds. Subsequently, the samples were exposed totetramethylsilane (TMS) plasma at a TMS flow rate of 150 SCCM but noadded oxygen; this corresponds to an atomic ratio of oxygen to siliconof about 0. The pressure in the chamber was 25 mTorr, and the RF powerof 1000 Watts was used for 10 seconds.

Resin Processing, Lamination and Curing

The resin formulations shown above in Table 2 were added to apolypropylene cup and mixed for 30 sec at 2500 rpm until homogenous in aSpeed Mixer (Flacktek). The formulations were coated using a notch barwith a 5 mil gap on a microstructured release liner described above. Thefilms were dried at 120° C. in an oven for four minutes until the filmformed a tacky gel. Sections of the film were cut out and laminated toglass slides with a hand roller, pre-baked at 60° C. in a convectionoven for 30 minutes to build adhesion, and then UV cured with a Fusion HBulb, 300 W/in intensity 2 passes at 30 feet/min. The glass/film toolstack was placed back in the oven at 120° C. for a post thermal bake tocomplete the curing process, then the microstructured release tool wasremoved, leaving behind the inverted pattern of microstructured toolingfilm on the substrate.

Test Methods Test Method 1: Transmission, Haze and Clarity

The measurement of average % transmission, haze and clarity wasconducted with a haze meter (BYK Gardiner, under the trade designation“BYK Hazegard Plus, Columbia, Md.”) based on ASTM D1003-11.

Test Method 2: Microstructure Thermal Stability Test

After peeling the nanostructured tooling film, the fully curednanostructures adhere to the substrate form an optical diffractionpattern that can be viewed with the naked eye. The glass slides wereplaced on a hotplate under nitrogen set at 100° C. for 15 minutes.Pictures of the glass slide were taken before and after the test and theoptical diffraction pattern of each was compared side by side. If nochange was observed in the optical diffraction of the nanostructuresafter all these tests, the resin formulation was considered to “Pass.”If the sample passed, the same procedure was followed with the samesample, except the heating was performed up to 230° C.

Test Method 3: Peel Adhesion

Peel adhesion is the force required to remove a coated flexible sheet ofmaterial from a test panel measured at a specific angle and rate ofremoval. Isopropyl alcohol was used to clean the glass prior to filmapplication. The samples were cut into 1″ wide strips. After laminationand prior to testing, the samples were equilibrated at a roomtemperature, 23° C. and relative humidity of 50%, for 15 minutes. Peeladhesion was measured as a 180 degree peel back at a crosshead speed of12 in/min using IMASS 2100 Slip/Peel Tester (IMASS, Inc., Accord,Mass.). The peel adhesion force is reported as an average of threereplicates, in ounces per inch.

Test Method 4: Parallel Plate Rheometer

Resin formulations were coated using a notch-bar at 5 mil dry thicknesson a release liner, and then cured at 120 C as described above. Multiplehandspreads were then laminated on top of themselves in order to achievea dry thickness of 30 mil. A TA Instruments (New Castle, Del.) DiscoveryHybrid Rheometer was run from −65 to 170° C. at 1 rad/sec with theadhesive in between 8 mm diameter parallel plates.

Test Method 5: Glass Transition Temperature

All examples and comparative examples were cured to the C-stage usingultraviolet radiation in a Fusion UV processor (Hereus, Gaithersburg,Md.) using a H-bulb and an exposure dose of 1 J/cm².

To measure the glass transition temperature, the cured films were cut to5 mm width and clamped into TA Instruments Q800 Dynamic MechanicalAnalyzer (DMA). The experiment was run in tension mode at a temperaturerange from 0° C. to 250° C. at a strain amplitude 5 micrometers, afrequency of 1 Hz, and a heating rate of 2° C./min. The glass transitiontemperature was defined by the peak of the tan delta curve.

Test Method 6: Thermal Decomposition Temperature

Pieces of the fully cured resins (about 2 mg each) were placed in atared aluminum pan inside a Q500 Thermogravimetric Analyzer from TAInstruments (New Castle, Del.). The heating rate selected was 10° C./minup to 550° C. The decomposition temperature was defined as thetemperature at which the resin has decomposed to 95% of its originalweight.

Results

Comparative Example 1 and 2 were prepared using linear thermoplasticpolymers in combination with multifunctional acrylate tackifiers. Thesewere compared to Example 1 and Example 2, which use a crosslinked epoxyin combination with multifunctional acrylate tackifiers and adhesionpromoters. Tests were performed to check for adhesive properties in thefilms' B-stage and high temperature performance at the films' C-stage.

Initial screening was performed using thermal stability tests describedabove in Test Method #2. Optical diffraction from the microstructure wasobserved to disappear after 100° C. for 15 minutes in ComparativeExample 1. This resin was excluded from future processing and analysis.Comparative Example #2 passed the 100 C thermal stability bake test, butfailed the 230° C. thermal stability test. Examples 1 and 2 passed bothtests and were evaluated further.

TABLE 3 Microstructure Thermal Stability Results CE1 CE2 E1 E2 100° C.Fail Pass Pass Pass Microstructure Thermal Stability 230° C. Fail FailPass Pass Microstructure Thermal Stability

Transmission and Haze Measurements, Glass Transition Temperature andThermal Decomposition Temperature analysis was performed of the fullycured resin samples that passed the 100° C. Microstructure ThermalStability Test. Results are shown in Table 4. All resin formulationsshowed a high transmission and low haze. A major difference betweenthese resin formulations is their thermal decomposition temperature.CE1, using a thermoplastic component, begins to decompose at 215° C. andthe optical diffraction resulting from the microstructures completelydisappeared by 230° C. E1 and E2 both have decomposition temperaturesgreater than 300° C. The high decomposition temperature in combinationwith glass transition temperatures greater than 150° C. lead to enhancedhigh temperature structural performance. CE2 shows two glass transitiontemperatures, one at 2 degrees C. and a second at 168 degrees C., thusCE2 has at least one glass transition temperature of less than 150degrees centigrade.

TABLE 4 C-Stage Resin Properties CE2 E1 E2 Transmission (% T) 93.4 93.493.3 Haze (%) 0.90 0.47 0.67 Decomposition Temperature at 5% 215 315 350Weight Loss (TGA, ° C.) Glass Transition Temperature (° C.) 2 and 197165 168

Table 5 shows the Peel Adhesion, Glass Transition Temperature andParallel Plate Rheometer Test results of the B-staged films. The resultsshow that E1 and E2 have higher storage modulus and also higher glasstransition temperature values (above 150 degrees C.), compared to CE2.E1 and E2 also had lower peel adhesion values than CE2. However, it wassurprising that E1 and E2 were able to have the combination of theadhesive properties when partially cured to enable wet-out on thereceptor substrate, and maintaining high temperature structuralperformance when fully cured on the substrate and removed from thetooling film mold.

TABLE 5 B-Stage resin properties CE2 E1 E2 Storage Modulus 3535 4005937705 G′ at 25 C., 1 Hz (Pa) Glass Transition Temperature −50 −16 −15(Tg) (° C.) Peel Adhesion ((oz/inch) 1.85 ± 1.5 0.37 ± 0.02 1.64 ± 0.15

Thus, embodiments of METHOD OF FORMING DUAL-CURE NANOSTRUCTURE TRANSFERFILM are disclosed.

All references and publications cited herein are expressly incorporatedherein by reference in their entirety into this disclosure, except tothe extent they may directly contradict this disclosure. Althoughspecific embodiments have been illustrated and described herein, it willbe appreciated by those of ordinary skill in the art that a variety ofalternate and/or equivalent implementations can be substituted for thespecific embodiments shown and described without departing from thescope of the present disclosure. This application is intended to coverany adaptations or variations of the specific embodiments discussedherein. Therefore, it is intended that this disclosure be limited onlyby the claims and the equivalents thereof. The disclosed embodiments arepresented for purposes of illustration and not limitation.

1. A method of forming a transfer film comprising: coating a backfillcomposition onto a structured non-planar template layer to form abackfill layer conforming to the non-planar structured surface, thebackfill composition comprising: multifunctional epoxy monomers;multifunctional acrylate monomers; curing the multifunctional epoxymonomers to form a cross-linked epoxy polymer with the multifunctionalacrylate monomers dispersed therein and forming a transfer film.
 2. Themethod according to claim 1, further comprising applying a release lineronto a planar major surface of the backfill layer wherein the backfilllayer is between the release liner and the structured non-planar releasesurface.
 3. The method according to claim 1, wherein the backfillcomposition comprises a molecule having acrylate and epoxyfunctionalities.
 4. The method according to claim 1, wherein thetransfer film has a glass transition temperature value that is less than25 degrees centigrade.
 5. The method according to claim 1, wherein thecross-linked epoxy polymer comprises cycloaliphatic multifunctionalepoxy groups.
 6. The method according to claim 1, wherein themultifunctional acrylate monomers comprise cycloaliphaticmultifunctional acrylate groups.
 7. The method according to claim 1,wherein the curing step comprises cationic curing of the multifunctionalepoxy monomers to form the cross-linked epoxy polymer without curing themultifunctional acrylate monomers.
 8. The method according to claim 1,wherein the curing step comprises thermally initiated cationic curing ofthe multifunctional epoxy monomers to form the cross-linked epoxypolymer without curing the multifunctional acrylate monomers.
 9. Themethod according to claim 1, wherein the curing step comprisesphoto-initiated cationic curing of the multifunctional epoxy monomers toform the cross-linked epoxy polymer without curing the multifunctionalacrylate monomers.
 10. A method of forming a transfer film comprising:coating a backfill composition onto a structured non-planar templatelayer to form a backfill layer conforming to the non-planar structuredsurface, the backfill composition comprising: multifunctional epoxymonomers; multifunctional acrylate monomers; curing the multifunctionalacrylate monomers to form a cross-linked acrylate polymer with themultifunctional epoxy monomers dispersed therein and forming a transferfilm.
 11. The method according to claim 10, further comprising applyinga release liner onto a planar major surface of the back fill layerwherein the backfill layer is between the release liner and thestructured non-planar release surface.
 12. The method according to claim10, wherein the backfill composition comprises a molecule havingacrylate and epoxy functionalities.
 13. The method according to claim10, wherein the transfer film has a glass transition temperature valuethat is less than 25 degrees centigrade.
 14. The method according toclaim 10, wherein the cross-linked acrylate polymer comprisescycloaliphatic multifunctional acrylate groups.
 15. The method accordingto claim 10, wherein the multifunctional epoxy monomers comprisecycloaliphatic multifunctional epoxy groups.
 16. The method according toclaim 10, wherein the curing step comprises free-radical curing of themultifunctional acrylate monomers to form the cross-linked acrylatepolymer without curing the multifunctional epoxy monomers.
 17. Themethod according to claim 10, wherein the curing step comprisesthermally initiated free-radical curing of the multifunctional acrylatemonomers to form the cross-linked acrylate polymer without curing themultifunctional epoxy monomers.
 18. The method according to claim 10,wherein the curing step comprises photo-initiated free-radical curing ofthe multifunctional acrylate monomers to form the cross-linked acrylatepolymer without curing the multifunctional epoxy monomers.
 19. A methodcomprising: laminating the backfill layer of the transfer film accordingto claim 1 onto a receptor substrate; and curing the multifunctionalacrylate monomers to form a cross-linked acrylate polymerinterpenetrating the cross-linked epoxy polymer defining a fully curedlight transmission layer.
 20. The method according to claim 19, whereinthe cross-linked epoxy polymer is cured via a cationic mechanism and themultifunctional acrylate monomers is cured via a free-radical mechanism.21. The method according to claim 19, further comprising removing thestructured non-planar template layer from the fully cured lighttransmission layer.
 22. The method according to claim 21, wherein thefully cured light transmission layer has a haze value of less than 2%and a visible light transmission greater than 85% and a decompositiontemperature greater than 250 degrees centigrade.
 23. The methodaccording to claim 19, wherein the curing step comprises thermallyinitiated free-radical curing of the multifunctional acrylate monomersto form the cross-linked acrylate polymer interpenetrating thecross-linked epoxy polymer defining a fully cured light transmissionlayer.
 24. The method according to claim 19, wherein the curing stepcomprises photo-initiated free-radical curing of the multifunctionalacrylate monomers to form the cross-linked acrylate polymerinterpenetrating the cross-linked epoxy polymer defining a fully curedlight transmission layer.
 25. A method comprising: laminating thebackfill layer of the transfer film according to claim 10 onto areceptor substrate; and curing the multifunctional epoxy monomers toform a cross-linked epoxy polymer interpenetrating the cross-linkedacrylate polymer defining a fully cured light transmission layer. 26.The method according to claim 25, wherein the cross-linked epoxy polymeris cured via a cationic mechanism and the multifunctional acrylatemonomers is cured via a free-radical mechanism.
 27. The method accordingto claim 25, further comprising removing the structured non-planartemplate layer from the fully cured light transmission layer.
 28. Themethod according to claim 25, wherein the fully cured light transmissionlayer has a haze value of less than 2% and a visible light transmissiongreater than 85% and a decomposition temperature greater than 250degrees centigrade.
 29. The method according to claim 25, wherein thecuring step comprises thermally initiated cationic curing of themultifunctional epoxy monomers to form the cross-linked epoxy polymerinterpenetrating the cross-linked acrylate polymer defining a fullycured light transmission layer.
 30. The method according to claim 25,wherein the curing step comprises photo-initiated cationic curing of themultifunctional epoxy monomers to form the cross-linked epoxy polymerinterpenetrating the cross-linked acrylate polymer defining a fullycured light transmission layer.